Process for production of calcium hypochlorite bleach liquor



Dec. 20, 1960 w. M. OSBORNE ET AL 2,965,443

PROCESS FOR PRODUCTION OF CALCIUM HYPOCHLORITE BLEACH LIQUOR Filed Aug.13, 1958 3 Sheets-Sheet 1 mm .m on W W W IN mmuuoma M om A: o 02:65 5 mm8 T H 0% mm mm 9 4 uoEw 531. 5&05 8 0m .5645 Q 6%,: 2233 TN m fixi w 523w/k 5w 86 v m m a E mm l at 8 mm K 2 k A 5 30528 wfimwfi uzEoiu t qo r pM. D 2 Mai mm zoFzuBm w mm mm ww EEjm m2: Bxim mm 9 o N AVAILABLECHLORINE G.P.L.

Dec. 20, 1960 PROCESS FOR PRODUCTION OF CALCIUM HYPOCHLORITE BLEACHLIQUOR Filed Aug. 13, 1958 Sheets-Sheet 2 700 MV 48 e00 MV 44 580 MV 362 L I%/ 24 55o MV I2 500 MV CONCENTRATION OF" LIME SLURRY G.P.L.

Dec. 20, 1960 w. M. OSBORNE ET AL 2,965,443

PROCESS FOR PRODUCTION OF CALCIUM HYPOCHLORITE BLEACH LIQUOR Filed Aug.15, 1958 5 Sheets-Sheet 5 w v N mmmuo om 2 @2555 mm OF 1N. 3 mm mm b 8M2 m q 5G: ,(M

d R r 5N r .8 2 2 m. 5 l on 1 5:626 UZESIU S30E28 pm 2986 t -6 A J 552 9E5 zopzmhfi 2 A NN S 8v mm vm fim chlorine present.

PROCESS FOR PRODUCTION OF CALCIUM HYPOCHLORITE BLEACH LIQUOR Wesley M.Osborne, Fircrest, Wash., Dexter Edge, Jr., Lewiston, N.Y., and ArthurD. Johnston, Springfield, Oreg., assignors to Hooker ChemicalCorporation, Niagara Falls, N.Y., a corporation of New York Filed Aug.13, 1958, Ser. No. 754,814

2 Claims. (Cl. 23-86) This invention relates to a continuous process forproduction of calcium hypochlorite bleach liquor. More particularly,this invention relates to a continuous, automatic process for productionof semi-clarified calcium hypochlorite bleach liquor.

This is a continuation-in-part of our copending application, Serial No.550,546, filed December 2, 1955, now US. 2,889,199.

In the prior art method of preparing calcium hypo chlorite bleachliquor, milk of lime is chlorinated, in accordance with the followingreaction:

The calcium hydroxide is derived from the hydration of calcium oxidewhich in turn is produced by the roasting of naturally occurring calciumcarbonate. The latter is never found in a pure state, but containsforeign matter, some of which is of a siliceous nature, such as sand andis highly insoluble. The calcium hydroxide itself is of low solubilityand as milk of lime is largely in a state of suspension. In addition tothe insoluble matter above mentioned, there is always present a certainportion of insoluble carbonates, some of which may be a residue of theoriginal calcium carbonate. Additional calcium carbonate may be formedduring the hydration of the lime by absorption of carbon dioxide fromthe atmosphere. Unless this insoluble matter is removed from the bleachliquor before it is used in a paper pulp process, some of it will appearin the finished paper as specks, discolorations and rough spots. In theprior art it has been the practice to allow the sludge to settle anddecant 'ofi the clear liquor. This method of course involves the wasteof any excess undissolved calcium hydroxide that may be present. Thesettling of the sludge and decanting oil of the liquor is an operationusually requiring a period of approximately to 12 hours. Further, thissettling necessitates the installation of large capacity tanks andinvolves additional supervision, thus adding appreciably to the cost ofthe bleaching operation. When the suspension of lime in water ischlorinated to produce calcium hypochlorite which may be in solution,solids present or formed must be separated from the solution and thendiscarded if the process is not designed to handle this material.

If over-chlorination results, as often happens in a batch-type process,a deficiency in calcium hydroxide results and the following reactionoccurs:

(2) Ca(OCl) +2Cl +2H O- 4HOCl+CaCl The hypochlorous acid decomposesquite readily as follows:

After Reaction 3 has taken place a portion of the chlorine becomesunavailable, and thus it is clear that the favorable condition forpromoting Reaction 1 requires the presence of calcium hydroxide inexcess of the unreacted To prevent ReactionsZ and 3 it is customary touse an excess of calcium hydroxide often areas a 2,955,443 Patented Dec.29, 1950 ice as high as 10 percent. Another method of preventingReactions 2 and 3 consists in decreasing the amount of chlorine suppliedtoward the end of the reaction. The latter method is not particularlypractical since it is not representative of standardized manufacturingoperations and therefore requires especially close observation by veryskilled operators. Thus in the prior art, it has been difiicult tomaintain a process for the production of calcium hypochlorite whereinsuspended lime has not been present in the product, and wherein all ofthe chlorine and lime has been utilized.

It is the main object of this invention to provide a con tinuous,automatic process for the production of semiclarified calciumhypochlorite bleach liquor wherein stability and uniformity of bleachliquor are improved, thus resulting in a consistently better quality ofproduct. Further, it is an object of this invention to utilizesubstantially all of the chlorine and lime and thus to remove the lossesinherent with the conventional hatch systems. Still further, it is anobject of this invention to provide a more economical process whereinspace requirements, installation and maintenance costs are reducedconsiderably. Other objects will become apparent to those skilled in theart on consideration of the complete specification and claims.

These and related objects are accomplished by the present inventionwhich may be more easily understood by reference to the attacheddrawings. Figure l is a diagrammatic flow sheet of one preferredembodiment embraced within the scope of our invention; Figure 2 is agraph showing the variation of available chlorine (grams per liter) inthe product with variation in lime feed concentration (grams per liter).The oxidationre'duction potential of the calcium hypochlorite bleachliquor product was measured in millivolts using a silverplatinumelectrode cell at a temperature of '90 degrees Fahrenheit.

Referring to Figure l: Dilute slaked lime slurry feed 1 controlled byvalve 2 and water feed 3 controlled by valve 4 are mixed 5 to apredetermined concentration. The resultant lime slurry is transferredthrough line 6 by means of a pump 7 to a storage tank 8. A change in thelevel of the material in the storage tank is transmitted 9 to a levelindicator controller 10 which actuates the slaked lime feed controlvalve 2. The lime slurry is transferred from the storage tank 8 by meansof the pump 7 through line 6, and the feed is controlled by valve 11 tothe mixer 12. Chlorine feed 13 controlled by valve 14 is passedthrough'a barometric leg 15 into the mixer 12. The resultant mixture ispassed through a retention pipe 16 to a liquid cyclone classifier 17.The underfiow 18 of the classifier passes through a recycle cup 19 andthen through line 18 into the lime slurry line 6. A drain 28 may beprovided to remove the non-lime insolubles. The overflow liquid 21 fromthe classifier is fed through a degasser 22. Any gases present may bevented 23 to a recovery system not shown. The liquid stream 24 is passedthrough an electrode assembly 25 of an oxidation-reduction potentialcontroller 26. This instrument is preset at a value dependent upon theavailable chlorine desired in the finished bleach liquor and theconcentration of the lime slurry. The output 27 of this controller isused to regulate the lime slurry feed valve 11 to the mixer 12. The mainproduct stream 28 is passed to the product storage tank 29. The productmay be transferred by a pump 30 to a bleaching process 31. A minorportion of the product stream 32 may be passed through a gravityinstrument 33. A gravity controller 34 automatically controls 3 5 thewater flow valve 4. After passing through the gravity instrument thestream joins the main product stream 36, The level of the product in thestorage tank may be in communica that starting with a lime slurryconcentration from 25 to 50 grams per liter that any concentration from8 to 50 grams per liter of available chlorine in the product may beobtained by presetting the oxidation-reduction controller at a valuedetermined from the graph. For example if it were required to producefinished bleach liquor containing 28 to 30 grams per liter of availablechlorine from dilute lime slurry controlled at between about 31 and 33grams per liter respectively, the desired result may be accomplished bypresetting the potential controller at about 590 millivolts.

Referring to Figure 3: Figure 3 is identical with Figure 1, except thatthe output 27 of the electrometric controller 26 is used to regulate thechlorine feed valve 14, and the level of the product in the storage tank29 may be in communication through line 37 with a level indicatorcontroller 38 which will automatically regulate the lime slurry feedvalve 11.

We have now found a continuous process for the production ofsemi-clarified hypochlorite bleach liquor which comprises mixing acontrolled lime slurry feed and chlorine, and passing this mixturethrough a retention conduit for a time suflicient to effect the desiredchlorination. Then, the mixture so produced is passed through a liquidclassifier wherein the underflow of the classifier is recycled to thelime slurry feed and the overflow of the classifier is recovered ascalcium hypochlorite bleach liquor. A portion of this product is passedthrough a measuring means wherein said means provides an impulse to anelectrometric controller, said controller producing a corrective action,in accordance with said controller set point, to reposition the chlorinefeed valve thereby controlling the chlorine feed rate.

The following example further illustrates our invention but it is to beunderstood that the specific details given in the example have beenchosen for the purpose of illustration and are not intended to limit ourinvention excepT as defined in the appended claims.

Example 1 In a method similar to the foregoing description of theprocess, dilute lime slurry (30.5 grams per liter) controlled at about14 gallons per minute and at a temperature of 75 degrees Fahrenheit orless was fed into a stream of chlorine 13 (2 pounds per minute) which isunder pressure of 25 to 35 pounds per square inch gauge. Liquid chlorinemay be used where reliable means of accurate and safe control isavailable. The reaction mixture was passed through a pipe section 16 (15foot length, 2 inch diameter) to provide the violent turbulencenecessary for quick reaction. The pressure at the entrance to theclassifier was approximately pounds per square inch gauge. The mixturewas passed through a liquid cyclone classifier 17, such as the two-inchdiameter Dorr-Clone (porcelain Model P-50). The underfiow 18 (4 gallonsper minute and containing 18.5 grams per liter of calcium hydroxide) wasdischarged freely into a recycle line which returned the solids to thesuction side of the lime slurry pump. A drain 20 on the recycle line wasused to periodically purge the system of heavy non-lime particles whichgradually build up. The overflow 21 (10 gallons per minute containingparticles less than 50 microns) from the classifier was piped directlyinto a four-inch diameter degasser 22. The finished bleach liquor 24 wasconducted from the degasser to the calcium hypochlorite storage tank 29.A portion ofthe finished bleach liquor was transferred through anelectrode assembly 25 of an oxidation-reduction potential controller 26.The set point of the controller was about 640 millivolts usingcalomel-platinum electrodes; and under these conditions the feed line tothe calcium hypochlorite storage tank was analyzed and found to contain:30 grams per liter of available chlorine; 0.1 3

4 percent suspended solids; 0.0 gram per liter suspended calciumhydroxide; and 0.45 gram per liter dissolved calcium hydroxide.

Any method of mixing the lime slurry and chlorine, wherein the violentturbulence necessary for quick reaction and low volume hold-up isprovided, will be satisfactory. In order to insure the completion of theca1- cium hypochlorite reaction, a conduit which may be in the form of aloop or an S may be installed between the mixer and the liquid cycloneclassifier or a conduit of extended length may be used alone. Thisconduit is sized to produce turbulent flow and to provide a retentiontime preferably less than 10 seconds at the minimum expectant flow rate;for example, an S-shaped conduit of one-inch diameter standard pipe,twenty-six feet in length was satisfactory for a flow rate of thirteengallons per minute.

The liquid classifier is required to handle a relatively large flow ofliquid and of necessity the mixture contains lime and often othermaterials in suspension. It is necessary to separate the finished liquorfrom such suspended materials and this may be conveniently done in anytype of hydro-separating equipment which is of suflicient size andcapacity so that the overflow of finished bleach liquor is relativelyclear and relatively free from suspended materials and so that thehold-up time is comparatively short, for example 20 seconds or less. ADorr-Clone classifier (porcelain Model P-50) has met these requirements.The classifier underflow is allowed to discharge freely into a recycleline and since this liquid contains heavy particles, horizontal runsshould be avoided to prevent settling and possible plugging. Theunderflow containing unrcacted suspended lime particles and non-limeparticles larger than 50 microns is continuously recycled to the mixerfor further chlorination; thus the coarse lime is eventually consumedthrough reaction with some additional chlorine in each passage throughthe reaction zone. A drain on the recycle line is used to periodicallypurge the system of heavy nonlime particles which gradually build up.

The preferred retention time from the initial mixing of the chlorine andlime slurry 12 to the completion of the separation of the overflow 21and underflow 18 is between five and twenty seconds at the minimum flowrate. A retention time less than five seconds will not insure thecompletion of the calcium hypochlorite reaction, and a retention timegreater than twenty seconds while it will provide a satisfactoryproduct, the extended time will provide a process lag which is adetriment to satisfactory automatic control of the process.

The oxidation-reduction potential controller consists of a standardin-line type electrode assembly utilizing either silver-platinum orcalomel-platium electrode pairs. These electrodes are used as they donot show serious "potential deviation when the bleach liquor temperatureis varied; further, they were unaffected by variation in excessundissolved lime. The overflow steam of the liquid classifier or aportion thereof is passed through the electrode assembly. Theoxidation-reduction potential controller having a range of 400 to 1000millivolts is preset at a value dependent upon the concentration of thelime slurry feed and the available chlorine required in the finishedproduct, this value being determined from Figure 2. The slow solution ofcoarse particles of suspended lime in the product will result in anunsteady, unpredictable potential and therefore removal of theseparticles before measuring the potential is necessary. The process maybe controlled by pH methods since the pH changes rapidly at the reactionendpoint giving a curve similar in shape to curves; but oxidationpotential methods are preferred for reason of simplicity and accuracy.

A gravity controller on the finished bleach liquor steam controls thebleach liquor concentration between desired limits. In Figures 1 and 3,this control is accomplished by the controller 33 actuating the watercontrol valve 4 according to changes in gravity of the product. Apossible variation within the scope of this invention is the dilution ofthe calcium hypochlorite product to the desired value on completion ofthe classification step, rather than before the chlorination step. Anyinstrument which will control the product strength, such as aconductivity controller, may be used to obtain the desired results.

The sequence of instrument action which may result in a continuous,automatic process for the production of semi-clarified calciumhypochlorite bleach liquor is as follows: As the bleach liquor 28 flowsto a process 31 such as bleaching pulp, a decline in the level of thematerial in bleach liquor storage tank 20 is transmitted 37 to a levelcontroller 38 which actuates the lime slurry feed valve 11 to increasethe feed flow to the mixing zone 12 to provide more product. Theresultant increase in available lime in the product reflects quickly onthe oxidation-reduction potential recorder 26 which immediately actuatesthe chlorine feed valve 11 to the mixing zone to provide enough chlorinefor the increased lime. An increase in flow of lime slurry is recordedas a decline in the dilute slurry storage tank 8, thus the levelcontroller actuates the dilute slaked lime flow valve 2 to maintain theproper level in the dilute slurry storage tank. At this point the slakedlime feed to the waterslaked lime mixing zone 5 will increase above thedesired concentration and the resultant lime slurry concentration willincrease and therefore the product strength in line 32 will varyaccordingly from the desired value. This change in product strength isrecorded by the gravity controller 34 which automatically adjuststhrough line 35 the water feed valve 4 to bring the lime slurryconcentration back to the desired value. Any type of pneumatically orelectrically operated level, gravity and oxidation controllers may beemployed in the process of this invention wherein a change in the valueof the controlled variable is first asserted by a primary element andthis change is communicated by the measuring element to the controllingmeans. This controller mechanism then produces a corrective action inthe manipulated variable by energizing the power unit to reposition thefinal control element.

In the operation of the process of this invention it has been found thatthe process equipment may be constructed of the standard materials usedfor handling chlorine and calcium hypochlorite solutions below 110degrees centigrade. Examples of these materials are glass, Pyrex,rubber, plastic-lined steel, or other corrosion-resistant materials suchas Duriron.

It is to be understood that the above described arrangements are simplyillustrative of the application of the principles of the invention.Numerous other arrangements may be readily devised by those skilled inthe art which will embody the principles of the invention and fallwithin the spirit and scope thereof.

We claim:

1. A continuous process for the production of calcium hypochloritebleach liquor which comprises: mixing a controlled lime slurry feed anda controlled chlorine feed; passing said mixture through a retentionconduit for a time sufiicient to efiect the desired chlorination; thenpassing said mixture so produced through a liquid cyclone classifier;withdrawing the underfiow of said classifier and recycling saidunderfiow to the lime slurry feed; withdrawing the overflow of saidclassifier and recovering the calcium hypochlorite bleach product soproduced; the concentration of said product being controlled by passinga portion of said product through a means to measure electricalconductivity of the product liquor said means providing an impulse to anelectrometric controller, said controller producing a corrective actionin accordance with said controller set point to reposition the chlorinefeed valve thereby controlling the fiow of chlorine feed.

2. A continuous, automatic process for the production of calciumhypochlorite bleach liquor which comprises: mixing a controlled dilutelime slurry feed and a controlled water feed; passing said mixturethrough a controlled lime slurry feed valve; mixing said controlled limeslurry feed and a controlled chlorine feed; passing said mixture througha retention conduit for a time sufiicient to effect the desiredchlorination; then passing said mixture so produced through a liquidcyclone classifier; withdrawing the underflow of said classifier andrecycling said underflow to the lime slurry feed line prior to thecontrolled lime slurry feed valve; withdrawing the overfiow of saidclassifier and recovering the calcium hypochlorite bleach product soproduced from a product stream; passing a portion of said productthrough an electrode assembly, said assembly providing an impulse to anoxidation-reduction potential controller, said controller producing acorrective action in accordance with said controller set point toreposition the chlorine feed valve thereby controlling the chlorinefeed; passing a second portion of the product through a means forproviding an impulse to a gravity controller, said gravity controllerproducing a corrective action to reposition the water feed valve therebycontrolling the gravity of the product in said last named means; passingthe total combined recovered product through a means for providing animpulse to a level controller, said level controller producing acorrective action to reposition the lime slurry feed valve therebycontrolling the product level in said last named means; said dilute limeslurry feed being controlled by passing said feed through a means forproviding an impulse to a level controller, said level controllerproducing a corrective action to reposition the dilute lime slurry feedthereby controlling the lime slurry level in said last named means.

References Cited in the file of this patent UNITED STATES PATENTS Helleret al Mar. 4, 1952 Osborne et al June 2, 1959 OTHER REFERENCES

1. A CONTINUOUS PROCESS FOR THE PRODUCTION OF CALCIUM HYPOCHLORITEBLEACH LIQUOR WHICH COMPRISES: MIXING A CONTROLLED LIME SLURRY FEED ANDA CONTROLLED CHLORINE FEED, PASSING SAID MIXTURE THROUGH A RETENTIONCONDUIT FOR A TIME SUFFICIENT TO EFFECT THE DESIRED CHLORINATION, THENPASSING SAID MIXTURE SO PRODUCED THROUGH A LIQUID CYCLONE CLASSIFIER,WITHDRAWING THE UNDERFLOW OF SAID CLASSIFIER AND RECYCLING SAIDUNDERFLOW TO THE LIME SLURRY FEED, WITHDRAWING THE OVERFLOW OF SAIDCLASSIFIER AND RECOVERING THE CALCIUM HYPOCHLORITE BLEACH PRODUCT SOPRODUCED, THE CONCENTRATION OF SAID PRODUCT BEING CONTROLLED BY PASSINGA PORTION OF SAID PRODUCT THROUGH A MEANS TO MEASURE ELECTRICALCONDUCTIVITY OF THE PRODUCT LIQUOR SAID MEANS PROVIDING AN IMPULSE TO ANELECTROMETRIC CONTROLLER, SAID CONTROLLER PRODUCING A CORRECTIVE ACTIONIN ACCORDANCE WITH SAID CONTROLLER SET POINT TO REPOSITION THE CHLORINEFEED VALVE THEREBY CONTROLLING THE FLOW OF CHLORINE FEED.